http://travel.state.gov/family/adoption/country/country_369.html#sThis page has an alphabetized list of links to description of all the countries that have adoption programs. Sri Lanka is there, as is Thailand. You'd have to check on any others. This information will tell you if a certain country even allows foreign adoptions and what the requirements and procedures are.
However, just be aware that in catastrophes like this there are normally many, many families willing to adopt one of the orphans. And usually the country involved doesn't have a system in place to respond to the number of requests. Plus they are normally reluctant to place the children internationally, which is understandable. These children have already lost their parents, their homes, and everything else familiar to them. It would be extremely difficult for them to lose their country and language as well. And it would be a double loss to the country to have the death of the parents followed by the mass exit of the children. Often, other citizens of that country or the childrens' relatives are very willing to adopt the children who need families. That's probably the best-case scenario for all.
My husband and I have adopted a child from China, so I'm definitely an advocate of international adoption. However, because I know the process, I also know that it can easily become chaotic and corrupted. Plus, even though the would-be adoptive parents have the best and highest intentions, every adoption and especially international ones, involve a great amount of loss to the child. That has to be weighed against the situation and future outlook of that child's life without a family. You also have to consider whether or not you are prepared to handle the issues that invariably come with an adoption, compounded by cultural and language differences and emotional trauma caused by the tragedy. It's a life-changing decision.
However, even if you can't adopt one of these orphaned children, I think it's a good reminder that there are many, many orphans all over the world tonight who dream of having a family. And if you are able to become that family for even one of them, then at least some good will have come of this horrible disaster.
Peace.